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Singh R.S.,Punjabi University | Saini G.K.,Punjabi University | Kennedy J.F.,Advanced Science and Technology Institute
Carbohydrate Polymers | Year: 2010

Pullulanase showed significant improvement in thermal stability after covalent immobilization on Duolite XAD761. Optimum temperature of immobilized enzyme was 60 °C, which was 10 °C higher than the free enzyme. Apparent Km values for pullulan, soluble starch and dextran were 4.4, 20 and 50 mg mL-1, respectively. Mn2+ and Ca2+ showed 2.0- and 2.2-fold increase in enzyme activity. Activation energy (Ea) of immobilized biocatalyst was 22.38 kJ mol-1. Thermodynamic parameters (ΔH*, ΔG*, ΔS*) for irreversible inactivation of immobilized pullulanase at different temperatures (60-70 °C) were also determined. D-value was maximum (95.95 h) at 60 °C and temperature quotient (Q10) was 1.29. Immobilized biocatalyst was effectively used for pullulan hydrolysis in a batch system. Stationary phase in hydrolysis (95.70 ± 1.36%) was reached after 300 min at 125 rpm. Pullulan hydrolysis yielded 4.21 ± 0.06% reducing sugars under optimal conditions. Immobilized biocatalyst was successfully recycled for 33 batches, but the enzyme activity was reduced to half after 25th cycle. © 2010 Elsevier Ltd. All rights reserved. Source


Singh R.S.,Punjabi University | Saini G.K.,Punjabi University | Kennedy J.F.,Advanced Science and Technology Institute
Carbohydrate Polymers | Year: 2010

Pullulan production was carried out at shake-flask level and purified with isopropanol precipitation using single-step purification strategy. Purified pullulan obtained was used for preparing maltotriose syrup using pullulanase. Pullulanase was subjected to kinetic and thermodynamic characterization before its use for pullulan hydrolysis. Pullulanase exhibited considerable activity between pH 5 and 6, with an optimum pH of 5.0. It remained stable (100%) for 6 h at optimum temperature of 50 °C. Mn2+ and Ca2+ showed 1.8 and 2.1 times increase in pullulanase activity. Pullulanase effectively hydrolyzed pullulan, soluble starch and dextran. Decimal reduction time (D value) was 76.77 h at 50 °C and Z value was 12.5 °C for pullulanase. Thermodynamic parameters (ΔH*, ΔG*, ΔS*) for irreversible inactivation of free pullulanase at different temperatures (50-70 °C) were also determined. In a batch system, pullulanase hydrolyzed 94.25 ± 1.83% of purified pullulan and the resultant syrup contained 3.77 ± 0.07 mg/mL of maltotriose. Thus far, there is no report on thermodynamics of irreversible inactivation of pullulanase for the hydrolysis of pullulan. © 2009 Elsevier Ltd. All rights reserved. Source


Singh R.S.,Punjabi University | Saini G.K.,Punjabi University | Kennedy J.F.,Advanced Science and Technology Institute
Carbohydrate Polymers | Year: 2011

Pullulanase covalently immobilized on Duolite XAD761 has been used for developing a continuous flow reactor for the hydrolysis of pullulan. Packed bed reactor containing 34.10 U of immobilized biocatalyst with feeding of pullulan solution (0.44%, w/v) at a flow rate of 5 mL h-1 supported maximum pullulan hydrolysis at 60 °C. The reactor was run continuously for 32 days and immobilized biocatalyst lost half of its original activity after 31 days of continuous operation at 60 °C. The volumetric productivity and yield of reducing sugars were 3.38 ± 0.02 g L-1 h-1 and 4.40 ± 0.01 mg mL-1, respectively during the beginning of the hydrolysis. The developed immobilized biocatalyst has shown good operational and mechanical stability and can be successfully used for the hydrolysis of pullulan in a continuous system. Literature survey reveals no report on continuous hydrolysis of pullulan using whole cells or immobilized enzyme. © 2010 Elsevier Ltd. All rights reserved. Source


Ma Z.,Ocean University of China | Yang L.,Ocean University of China | Yan H.,Ocean University of China | Kennedy J.F.,Advanced Science and Technology Institute | Meng X.,Ocean University of China
Carbohydrate Polymers | Year: 2013

The effects of chitosan and oligachitosan on resistance induction of peach fruit against brown rot caused by Monilinia fructicola were investigated. Both chitosan and oligochitosan showed significant effect on controlling this disease. Moreover, chitosan and oligochitosan delayed fruit softening and senescence. The two antifungal substances enhanced antioxidant and defense-related enzymes, such as catalase (CAT), peroxidase (POD), β-1,3-glucanase (GLU) and chitinase (CHI), and they also stimulated the transcript expression of POD and GLU. These findings suggest that the effects of chitosan and oligochitosan on disease control and quality maintenance of peach fruit may be associated with their antioxidant property and the elicitation of defense responses in fruit. © 2013 Elsevier Ltd. All rights reserved. Source


Chang C.,Hubei University | Zhang L.,Hubei University | Zhou J.,Hubei University | Kennedy J.F.,Advanced Science and Technology Institute
Carbohydrate Polymers | Year: 2010

Hydrogels have been successfully prepared from cellulose in NaOH/urea aqueous solution by using epichlorohydrin (ECH) as a cross-linker, and via heating and freezing methods. Structure and properties of the hydrogels were measured with UV-vis spectroscopy, SEM, XRD, solid-state 13C NMR, rheometry and water absorption testing. The results indicated that hydrogels prepared by heating displayed macroporous inner structure, while fiber-like structure could be observed in the hydrogels prepared by freezing. The light transparency and equilibrium swelling ratio of the hydrogels decreased, while the reswelling water uptake and the storage modulus increased, with an increase of the cellulose content. Compared with the hydrogels post-treated by freezing, the hydrogels prepared by heating displayed better light transmittance, higher equilibrium swelling ratios and reswelling water uptakes, and relatively weaker mechanical strength. Therefore, the structure and properties of the hydrogels could be adjusted by changing the cellulose content and the post-treatment methods. © 2010 Elsevier Ltd. All rights reserved. Source

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